TOP 3: BROWSER BASED GAMES
Action
Phosphor - Rasterwerks
This is a one player very fun 1st person shooter. Rare to find as a browser based game, 1st person shooters are very enjoyable (such as Halo, Medal of Honor, Warrock, etc.)
http://www2.rasterwerks.com/game/phosphor/beta1.asp
Instantaction
Extreme breakthrough in multiplayer action. Since it is browser based it has opened a whole realm of gaming to those who wish not to take up their computers memory or risk it catching a virus. Currently their are 4 games to choose from: 1. Think Tanks 2. Marble Blast 3. Zap! 4. Rokkit Ball
www.instantaction.com
XGen - Stick Arena
This game can be extremely fun, or terrible. Make sure you call up a friend or type with someone in the chat about playing it with them in a private room set up in the games lobby. Otherwise the game is full of hackers and is not 2 seconds of your time.
http://www.xgenstudios.com/play/stickarena
RPG
Runescape
Huge community, although i personally have not given it much of a chance I hear its fun and very addictive.
www.runescape.com
Dragon Fable
Extremely fun. Limitless quests and the leveling system is one of my favorites. (From the creators of Adventure Quest)
http://www.dragonfable.com
Gods Of Time
You get to freely walk around and battle wild monsters and other players. You gotta at least check this one out!
http://www.godsoftime.com
Social
Gaia Online
Create a character and post on the forums or roam in the game and chat. You can even add furniture in your house and even play games to earn Gaia $$$.
Habbo Hotel
I am not going to lie to you this game is REALLY FUN! But be forewarned it is very addictive, and you have to pay to get furniture for your room that you can gamble and trade. Basically its a an addictive gambling and hustling smiley town. NEVER CLICK ACCEPT TRADE UNLESS THEY HAVE FURNITURE IN. If you just want to talk and harass people though then this is the game to do it.
World Of Words 2
A chatroom where it takes 2 seconds to get in and 1 hour to figure out what the hell it is. Great for chit chatting but almost a promise that it will be all diff. people the next time you play.